The present invention relates to brushless DC motor driven cryogenic refrigeration systems, and particularly to such systems which are designed to be portable and small in size and weight and thus useful in aircraft and armored vehicles and tanks used by the armed forces. In such vehicles, cryogenics are used for various purposes such as for cooling the semiconductor chips used in laser range finders, chemical agent detectors, and infrared systems.
In applications such as the above, in various vehicles, the electronic circuit which is used with the brushless DC motor for switching the stator-armature winding currents in synchronism with the rotation of the motor rotor must receive special protection from the operating atmosphere, as well as mechanical protection. The normal procedure for providing such protection is to encapsulate the electronic circuit within an enclosure filled with a potting compound, or hermetically sealed in a gaseous atmosphere. Both of these arrangements involve considerable additional expense, and are subject to problems of possible failure, especially if the exterior enclosure for the circuit is mechanically damaged.
Accordingly, it is one object of the present invention to provide an improved brushless DC motor in combination with a cryogenic refrigeration system in which the separate enclosure for the electronic circuit may be eliminated.
Another problem with existing brushless DC motor-driven cryogenic refrigeration systems is that the motor itself is enclosed within a common housing with the cryogenic refrigerant compressor while the electronic circuit for the motor is housed outside of that housing. The refrigerant used is usually helium. With this arrangement, there are usually eight electrical connections which must be carried through the housing wall between the electronic circuit and the DC motor. Unfortunately, the helium, which is under considerable pressure, (the pressure normally varies between 400 and 900 pounds per square inch), is difficult to contain within the housing and is especially likely to leak out around the eight connections that are carried through the housing wall.
Accordingly, it is another object of the present invention to provide a brushless DC driven cryogenic refrigeration system in which the number of electrical connections which must be carried through the wall of the housing containing the refrigerant is substantially reduced.
Still another problem in portable brushless DC motor driven cryogenic refrigeration systems which are used for vehicles is that the electrical connection leads from the electronic circuit when used with the brushless DC motor to the motor itself cause the radiation of electrical signals which can interfere with the operation of other apparatus such as radio receivers.
Accordingly, it is another object of the present invention to shorten the leads between the electronic field switching circuit of the brushless DC motor and the motor itself in a cryogenic refrigeration system.
Further objects and advantages of the invention will be apparent from the following description and the accompanying drawings.